This invention relates to an apparatus for aligning and bonding a preperforated tape to perforated material, such as motion picture film and the like, and more particularly to an improvement in a pressure roller for bonding pressure adhesive tape with perforations over sprocket holes in the film.
In ordinary use, the perforations along motion picture film are engaged by drive sprockets or a shuttle arm used to feed the film through a utilization system. As the film is used again and again for its intended purpose, film tends to tear around the perforations, particularly at the beginning and end of a reel of film. In those, and other cases of damage to the perforations, it is desirable to repair the film by bonding a strip of preperforated tape along the film where damage has occurred, with the perforations of the tape aligned with the sprocket holes of the film.
U.S. Pat. No. 3,959,048 discloses an arrangement for bonding preperforated repair tape to motion picture film with the precision required to align the tape perforations with the film perforations along the length of the tape, but the alignment system is complex, and leaves much to be desired. Improvements over that arrangement are disclosed in U.S. Pat. No. 4,026,756. The improvements deal primarily with the problem of aligning the perforations of the repair tape with the perforations of the film along the length of the film.
It has been determined that the asymmetrical sprocket shape disclosed in U.S. Pat. No. 4,026,756 is not required for synchronization, and may itself cause damage to the film since flat sides are provided on the sprocket to force alignment of perforations in the tape with perforations in the film. Instead, it has been found that symmetrical sprockets of the same configuration as sprockets in the film utilization system will best serve the need for alignment of repair tape without any risk of further damage to the perforations in the film. Alignment of the perforations in the repair tape with perforations in the film will be achieved, even though the film tends to shrink with age and other factors, as mentioned in the prior patents.
What is now recognized is the need to improve transverse alignment of the repair tape to maintain side edges of holes in the repair tape in line with side edges of holes in the film, and more particularly to assure firm bonding of the repair tape on the film along side edges of holes and between holes. In the first of the aforesiad patents, a pressure roller is used having "apertures" or recesses shaped and spaced to receive sprockets on the sprocket wheel, thereby to apply pressure to the adhesive tape all around a sprocket hole. This presented a problem in initial adjustment of the roller during the start of each repair run to assure that the sprockets are aligned with roller apertures. To avoid that problem, the pressure roller in the second one of the aforesaid patents is grooved, instead of apertured, but the repair tape between sprocket holes is then not subjected to pressure for good bonding. The problem is to apply pressure all around each sprocket hole.
The term "film" is used hereinafter to refer to any unrestricted length of material with aligned and evenly spaced perforations to be repaired, and the term "sprocket holes" is used hereinafter to refer to those holes. Motion picture film is, of course, a primary example, but the present invention is not to be construed to be limited to a film for motion pictures. The film may be a strip of material for other purposes as well.